This application relates generally to communications networks, and more particularly, to determining electrical properties of multi-wire communication lines.
Recently, there has been an increased demand for the subscriber lines of plain old telephone services (POTS""s) to carry high-speed digital signals. The demand has been stimulated by home access to both the Internet and distant office computers. Both types of access typically employ a POTS line as part of the path for carrying digital signals.
POTS""s lines were built to carry voice signals at audible frequencies and can also carry digital signals as tone signals in the near audible frequency range. Modern digital services such as ISDN and ADSL transmit data at frequencies well above the audible range. At these higher frequencies, POTS""s lines that transmit voice signals well may transmit digital signals poorly. Nevertheless, many telephone operating companies (TELCO""s) would like to offer ISDN and/or ADSL data services to their subscribers.
Telephone lines between a TELCO switch and subscribers"" premises are frequent sources of poor performance at the high frequencies characteristic of ISDN and ADSL transmissions. Nevertheless, high cost has made widespread replacement of these subscriber lines an undesirable solution for providing subscribers with lines capable of supporting ISDN and ADSL. A less expensive alternative would be to repair or remove only those subscriber lines that are inadequate for transmitting high-speed digital data.
To limit replacement or repair to inadequate lines, TELCO""s have placed some emphasis on developing methods for predicting which subscriber lines will support data services, such as ISDN and ADSL. Some emphasis has been also placed on predicting frequency ranges at which such data services will be supported. Some methods have also been developed for finding faults in subscriber lines already supporting data services so that such faults can be repaired.
Current methods for predicting the ability of subscriber lines to support high-speed digital transmissions are typically not automated, labor intensive, and entail test access at multiple points. Often, these methods entail using skilled interpretations of high frequency measurements of line parameters to determine data transmission abilities. At a network scale, such tests are very expensive to implement.
The present invention is directed to overcoming or, at least, reducing the affects of one or more of the problems set forth above.
In a first aspect, the invention provides a method of detecting a fault in a subscriber line having two wires with separate input impedances. The method includes driving the subscriber line from one end with an alternating voltage, making one-ended electrical measurements on the driven line, and determining from the measurements a quantity proportional to the phase difference of the two input impedances. The method also includes identifying a fault in response to the phase difference having a signature associated with the presence of a fault on the line.
In a second aspect, the invention provides a method of detecting a fault in a subscriber line having two wires. The method includes driving the two wires with an alternating voltage signal in a common mode configuration and measuring a phase difference between corresponding signals on the two driven wires. The method includes reporting a fault in response to the measured phase difference having a signature associated with presence of a fault on the line.
In a third aspect, the invention provides a method of determining whether a subscriber line can support a data service. The method includes performing one-ended electrical measurements on the line and determining from the measurements whether the line has a fault belonging to a set of types of faults. The set includes a split pair fault. The method also includes disqualifying the line for the data service in response to determining that the line has a fault from the set.
In a fourth aspect, the invention provides a method of providing digital data services. The method includes monitoring a plurality of subscriber lines by regularly performing one-ended electrical measurements on the lines and determining from the measurements whether one of the subscriber lines has a split pair.
In a fifth aspect, the invention features a method of providing digital data services. The method includes performing one-ended electrical measurements on a plurality of subscriber lines and determining from t he measurements whether one of the subscriber lines has a split pair.
In a sixth aspect, the invention provides a data storage medium encoding a computer executable program of instructions for performing one or more of the above described methods.
Various embodiments use test accesses, which provide data on low frequency electrical properties of subscriber lines, to make predictions about high frequency performance.